【作者】 李晓鸿；

【导师】 闵应骅；

【作者基本信息】 湖南大学 ， 计算机应用技术， 2010， 博士

【摘要】 无线自组织网络是在没有固定通信基础设施的情况下,由具有无线通信功能的节点自组织形成的网络。网络拓扑结构对网络的性能有着重大的影响,而如何简单快速构建和维护自组网拓扑结构、提高网络的传输性能、减少节点的能耗、增强网络的生存能力是拓扑控制研究的核心问题。设计分布式的、基于局部信息的拓扑控制协议,并与自组网通信协议相融合是拓扑控制技术走向实用化的关键问题。无线自组织网络拓扑控制是通过协调节点间各自传输范围,构建具有全局特性(如连通性)的网络拓扑结构,以减少节点的能耗或增加网络的传输能力为目的的技术。本文系统综述了拓扑控制算法迄今为止的主要研究成果,全面分析了目前拓扑控制算法的特点和性能,针对目前研究工作的不足,从定向天线自组网拓扑构建、拓扑结构干扰优化、自组网可生存拓扑管理和拓扑控制技术实用化这四个方面研究了拓扑控制问题。本文的创新性成果主要体现在以下几个方面:(1)研究拓扑控制与无线网络协议簇的关系,分析加入拓扑控制功能对相关通信协议的影响。提出了一种在MAC协议中嵌入拓扑控制算法的解决方案,并开发基于OPNET网络仿真平台的拓扑控制模拟模块,可用于拓扑控制算法对网络性能影响的仿真研究,为拓扑控制技术真正融入自组网协议奠定了坚实的基础。(2)通过对定向天线自组网连通问题定性和定量的分析研究,推导出保证拓扑图高概率连通的临界邻居数计算公式;在此基础上,提出了一种基于邻居数的分布式拓扑控制算法(DK-Neigh)。仿真实验说明,DK-Neigh算法可以保证整个网络的连通概率大于96%,节点的传输半径比初始值减少15%,提高自组网的能量有效性;当天线波束宽度小于60°时,DK-Neigh与全向天线拓扑K-Neigh拓扑控制算法相比,可使节点节能提高15%,表明节点采用波束宽度较小的定向天线,采用有效的拓扑控制算法,可获得比全向天线拓扑算法更好的节能性,提高网络的能量效率。(3)针对定向波束天线链路不对称问题,设计自适应波束天线模型,提出一种基于局部信息的集中式拓扑控制算法(BATC),协同调整所有节点的天线波束朝向和发射功率,进行拓扑控制。仿真实验表明BATC算法在保证网络连通的基础上,显著降低了节点的发射功率,提高了网络的吞吐量。(4)针对BATC算法不具有分布式性质的问题,本文进一步针对自适应波束天线,设计随机波束自组网模型,通过对随机波束自组网连通问题定性和定量的分析研究,推导出保证拓扑图高概率连通的临界邻居数计算公式;在此基础上,提出了一种基于随机波束天线的自组网拓扑控制协议(RBNTC)。仿真结果表明分布式协议RBNTC在维护网络高概率连通的同时,在提高网络节点节能性和网络传输性能方面效果显著。(5)根据无线通信的特点和网络协议的机制,提出了一种基于协议的网络干扰模型及度量方法,并提出了一种启发式的干扰最小化拓扑控制算法(ISPT)。该分布式算法基于新的干扰模型计算干扰值,构建局部的干扰最小化路径树,减小节点的发送功率。理论证明ISPT算法能保证网络连通,并使整个网络中节点间的路径干扰最小化。仿真结果表明ISPT算法显著降低了网络干扰,改善了网络性能。(6)研究无线自组网可生存性问题。提出面向网络可生存的容错拓扑控制设计策略。通过理论和实验求得保证网络多连通的关键邻居数,并提出一种基于邻居数的拓扑控制算法(k2TC),该分布式算法能构建并维护容错拓扑结构,算法简单且开销小。仿真结果验证了,在节点出现失效时,k2TC算法能够保证网络的抗毁性和有效性,使得无线自组网具有持续可生存的能力。更多还原

【Abstract】 Ad hoc wireless networks, or simply ad hoc networks, consist of a collection of geographically distributed nodes that communicate with one other over a wireless medium. Ad hoc networks differ from cellular networks in that there is no fixed infrastructure and the communication capabilities of the network are limited by the battery power of the network nodes. The topology of ad hoc networks,which is determined by positions and transmission ranges of nodes,has a significant effect on the network performance.Topology control deals with how to quickly deploy and maintain the network topology, increase the network capacity,reduce node energy consumption and enhance the network survivability. Furthermore, the integration of operational topology control techniques in the protocol stack is one of the main open research areas in this field.Topology control is the art of coordinating nodes’decisions regarding their transmitting ranges, in order to generate a network with the desired properties (e.g. connectivity) while reducing node energy consumption and/or increasing network capacity. In this thesis, the topology control problem and survey state-of-the-art solutions are proposed to tackle them. Topology control techniques in network simulation tool are implemented, and experimental results illustrate the effectiveness of topology control algorithms. However, several aspects related to topology control are not carefully investigated yet. In this research,the problem of topology control from four aspects are discussed about topology control for ad hoc networks using directional antennas, low-interference topology control, fault-tolerant topology control and implementation of topology control. The main contributions of this thesis are listed as follows:At first, a possible solution to integrate topology control mechanisms into the medium access control protocol is proposed. Through RTS/CTS message exchange, the MAC layer can trigger execution of the topology control protocol in case it detects new neighbors by overhearing the network traffic and analyzing the message headers. The integrated solution establishes a solid research foundation for topology control techniques. Then, OPNET network simulator is added processing module for topology control to the wireless MAC protocol and verif y its feasibility by experiments. Secondly, the topology control for ad hoc networks with directional antennas is investigated, in order to maintain network connectivity while reducing node energy consumption and increasing network capacity.A distributed neighbor-based topology control approach for ad hoc networks with steered beam antennas, referred to as the DK-Neigh, is proposed to maintain the outdegree of every node equal to or slightly below a specific value K. Quadrat statistical methods are employed to derive analytical expressions to determine the critical transmission range and neighbor number K. The approach can build the resulting communication graph with high probability connected. Extensive simulations are carried out, which show that the DK-Neigh is to achieve a high probability (more than 96 percent) of connectivity. If width of beam is smaller than 60 degree, average energy cost of nodes is reduced at least 15 percent than the topology control protocol K-Neigh using omni-directional antennas. Simulations show the DK-Neigh is more energy-efficient while maintaining network connectivity.A localized topology control algorithm for Ad hoc networks with steered beam directional antennas, referred to as the BATC, is proposed in this thesis. The topology is controlled not only by adjusting the transmission powers of nodes but also by changing the directional antenna’s direction. The centralized algorithm preserves the connectivity of the resulting topology. At the same time, the resulting network topology reduces energy consumption, decreases traffic interference and improves network throughput while transmission power reduced. Simulation results show that the proposed algorithm significantly improves the network performance.A tight lower bound for the critical neighbor number is deduced that is necessary to obtain an almost surely connected network with randomized beamforming on a bounded area of given size. In this thesis, a topology control protocol, referred to as the RBNTC, is proposed which is fully distributed, asynchronous, and localized. Not only does the constructed topology demonstrate significant reductions in the power required keeping the network connected, but also simulation results show that the proposed algorithm significantly improves the network performance.Thirdly, a new protocol interference model is presented as a measure to describe the interference of the entire network in this thesis. Furthermore, a distributed interference-avoidance topology control approximation algorithm, referred to as the ISPT, is proposed. The algorithm minimizes the interference in the network according to our metrics while preserving the connectivity of the resulting topology. The simulation results show that ISPT decreases interference and improves network capacity in terms of throughput.Finally, An arguement is proposed that survivability of topologies is not equivalence to connectivity of the multiply connected graph by illustrating some practical examples, then the concepts of network survivability into the topology of Ad hoc networks to obtain topology robustness and transmission capacity is introduced. Furthermore analytical expressions to determine the critical neighbor number for K-vertex connected topology are derived. A distributed neighbor-based topology control protocol, referred to as the k2TC, is proposed to maintain the degree of every node equal to or slightly below a specific value k when nodes fail, in a timely manner. The topology constructed under k2TC is high probability connected and bidirectional, which can be implemented at a reasonable cost. Simulation studies show that the resulting topology has good network survivability in terms of invulnerability and availability.更多还原